A resilient packet ring (RPR) is a scheme, defined in IEEE 802.17, for providing relief against a network failure. The RPR is a system in which multiple RPR relay devices are connected by two ring-type transmission paths for clockwise and anticlockwise transmissions and the two transmission paths are switched so as to bypass a transmission path and/or a station where a failure occurred, to thereby provide relief against a network failure. For example, refer to Japanese Laid-open Patent Publication No. 2006-279891 and International Publication Pamphlet No. WO 2005/015851.
As the communications media for the RPR, for example, SONET/SDH transmission paths are used. In this case, through the use of Generic Framing Procedure (GFP) and Virtual Concatenate (VCAT), an RPR frame is mapped on a SONET frame for transmission on the SONET/SDH transmission paths.
Also, in general, a line accommodating device that can provide large-capacity line services employs a shelf structure. An RPR relay device is realized in the form of a card, such as a station, and can be freely attached to and detached from the shelf of the line accommodating device. Thus, when the number of lines is increased, multiple stations may be accommodated in one shelf or stations accommodated in one shelf may belong to multiple RPR networks.
With such a configuration, when a failure occurs in one of the stations, which are RPR relay devices, an RPR failure recovery function works but a failure recovery function for yet another failure is lost. As opposed to it, a technology is disclosed in which a management unit detects a failure in each station and a connection path of stations where no failure is occurring is formed so as to bypass the station where the failure occurred. For example, refer to Japanese Laid-open Patent Publication No. 2006-279891.
However, in the related technologies noted above, when a failure occurs in a station during occurrence of a failure in the management unit, there is a problem in that switching to a connection path that bypasses the station where the failure occurred cannot be performed. Thus, when the network does not have a failure recovery function, such as an RPR, there is a problem in that the portion of the network which is in an interrupted state due to the station failure cannot be recovered from the interrupted state.
Also, when the network is an RPR network and a station where a failure occurred remains on the network, the RPR-based failure recovery function works, but the redundancy function is lost. Thus, there is a problem in that relief cannot be provided during occurrence of another failure.
Also, the management unit also performs overall line accommodating device control, such as control of each station for switching between the signal transmission paths on the network. Thus, when the management unit performs processing for detecting a failure through constant monitoring of the state of each station and/or processing such as re-formation of the connection path of the stations when a failure is detected, there is a problem in that a load on the management unit increases. As a result, it is conceivable that the functions of the management unit which include detection of a failure in each station and re-formation of a connection path cannot be fully exercised.